The present invention relates to an image sensing apparatus and reading apparatus and, more particularly, to the wiring structure of a contact image sensor which operates at a high speed (5 MHz or more).
In a contact image sensor (to be referred to as a CIS hereinafter), a reduction in size and power consumption can be attained depending on its structure. However, a CIS requires enough photoelectric conversion chips (to be referred to as CCD chips hereinafter) for the size of an image to be read and has a large number of CCD chips arranged in a line. In addition, an image signal as an analog signal has a range of 1 V with respect to the voltage of a driving signal (generally 5-V logic) due to a reduction in voltage of a photoelectric conversion chip. For this reason, to represent a monochrome image with 8-bit 256 grayscale levels, a precision as high as 1 LSB=about 4 mV is required. Therefore, it is hard to drive a conventional CIS at a high speed, and the driving frequency of a CCD chip is generally 1 to 2 MHz.
Demands for improvement in performance (demands for high resolution and high-speed reading) of an image reading apparatus have now arisen, and improvement in resolution of a CCD chip (600 dpi or more) and high-speed driving (5 MHz or more) has also been demanded for a CIS. Additionally, a method of improving actual reading speed by outputting a plurality of analog signals so as to realize higher speed (10 MHz or more) is expected to become the mainstream. Under the circumstances, the influence of logic signal noise on an analog signal cannot be neglected.
Moreover, in many cases, a CIS structurally employs an LED as a light source for reading, and chips themselves and their driving wiring lines are generally formed on a single substrate. At this time, driving control of an LED light source is performed by a combination of driving current and lighting time modulation (PWM control). The driving current is mostly larger than (twice or more) the CCD driving current, and switching noise which may occur in PWM driving would affect a CCD analog output signal.
In the prior art, to increase the S/N ratio of an analog signal from a CCD chip, techniques that pertain to the electrode arrangement of a switching element, the wiring structure accompanying the arrangement, and the like are suggested (see Japanese Patent Laid-Open Nos. 4-68571 and 5-14598).
However, in order to realize higher resolution and higher-speed operation of a CCD, a reduction in crosstalk of a plurality of stage outputs and prevention of superposition of digital noise on an analog signal are necessary. For this reason, it is very difficult to design a CIS substrate by conventional wiring techniques.
The present invention has been made to solve the above problem, and has as its object to provide an image sensing apparatus and, more specifically, an image sensing apparatus which, in a contact image sensor operating at a high speed (5 MHz or more), can prevent noise of a digital signal for light source driving and photoelectric conversion driving from being superposed on an analog signal, establish wiring pattern conditions suitable for reducing crosstalk between signals and suppressing variation in signal level, and output desirable image signals, and reliable reading apparatus including the same.
In order to solve the above problem, according to the present invention, there is provided an image sensing apparatus comprising a multi-layered substrate in which a photoelectric conversion chip and a wiring pattern of a digital signal which drives the photoelectric conversion chip are wired on a single substrate layer, wherein a wiring pattern of an analog signal which includes image information output from the photoelectric conversion chip and the wiring pattern of the digital signal which drives the photoelectric conversion chip are formed on separate substrate layers.
According to another aspect of the present invention, there is provided an image sensing apparatus comprising a multi-layered substrate in which a photoelectric conversion chip and a wiring pattern of a digital signal which drives the photoelectric conversion chip are wired on a single substrate layer, wherein a wiring pattern of an analog signal which includes image information output from the photoelectric conversion chip and the wiring pattern of the digital signal which drives the photoelectric conversion chip are formed on separate substrate layers so as not to vertically contact each other.
According to still another aspect of the present invention, there is provided an image sensing apparatus comprising a multi-layered substrate in which a photoelectric conversion chip and a wiring pattern of a digital signal which drives the photoelectric conversion chip are wired on a single substrate layer, wherein a width of a wiring pattern of an analog signal which includes image information output from the photoelectric conversion chip is equal to or more than a width of the wiring pattern of the digital signal which drives the photoelectric conversion chip.
According to still another aspect of the present invention, there is provided an image sensing apparatus comprising a multi-layered substrate in which a photoelectric conversion chip and a wiring pattern of a digital signal which drives the photoelectric conversion chip are wired on a single substrate layer, wherein a wiring pattern of an analog signal which includes image information output from the photoelectric conversion chip and the wiring pattern of the digital signal which drives the photoelectric conversion chip are wired on a single substrate layer, and a ground width between the wiring patterns is at least equal to or more than a width of the wiring pattern of the digital signal.
According to still another aspect of the present invention, there is provided an image sensing apparatus comprising a multi-layered substrate in which photoelectric conversion chips and a wiring pattern of a digital signal which drives the photoelectric conversion chip are wired on a single substrate layer, the multi-layered substrate having a plurality of analog output signal stages, the number of which is equal to or less than a number of the photoelectric conversion chips and being arranged to output an output signal from the photoelectric conversion chip to an outside of the image sensing apparatus through the plurality of analog output stages, wherein an analog output circuit is provided for each analog output stage, and each analog output circuit is comprised of one element.
According to still another aspect of the present invention, there is provided an image sensing apparatus comprising a multi-layered substrate in which a photoelectric conversion chip, a first wiring pattern of a digital signal which drives the photoelectric conversion chip, and a second wiring pattern of a driving signal which drives an LED light source for reading are wired on a single substrate layer, wherein each of the first wiring pattern and a third wiring pattern of an analog signal which includes image information output from the photoelectric conversion chip is formed to have one or more wiring states out of:
(1) a wiring state in which the first wiring pattern and third wiring pattern are formed on separate layers;
(2) a wiring state in which the first wiring pattern and third wiring pattern are formed on a single layer, and a ground width between the first and third wiring patterns is at least equal to or more than a width of the second wiring pattern; and
(3) a wiring state in which a high-frequency removal device is inserted at a ground portion of a driving signal which drives the LED light source, and
the second wiring pattern is electrically separated from the first and third wiring patterns.
According to the present invention, there is provided a reading apparatus which reads a document image, comprising the above-described image sensing apparatus, a document convey device disposed before and after the image sensing apparatus to position the document, a contact device which makes the document contact the image sensing device, and a control device which processes an output signal from the image sensing device to perform device control.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.